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A knowledge representation framework for the design
and the evaluation of a product variety
Antonio Giovannini
To cite this version:
Antonio Giovannini. A knowledge representation framework for the design and the evaluation of a
product variety. Computer Aided Engineering. Université de Lorraine, 2015. English. �tel-01109715�
THESE
Présentée pour l’obtention du titre de
Docteur de l’Université de Lorraine
en Automatique, Traitement du Signal et des Images, Génie Informatique par
Antonio Giovannini
A knowledge representation framework for the design
and the evaluation of a product variety
Soutenue publiquement le 16/1/2015 devant le jury composé de :
P
RESIDENT:
R
APPORTEURS:
C.
S
ALINESIM.
A
LDANONDOP
ROFESSEUR A L’U
NIVERSITEP
ARIS1
P
ANTHEON-S
ORBONNEP
ROFESSEUR A L’E
COLE DESM
INES D’A
LBI-C
ARMAUXM.
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RAJANOVICP
ROFESSEUR AU
NIVERSITY OFN
IS,
S
ERBIEE
XAMINATEURS:
M.
D
ASSISTIP
ROFESSEUR AP
OLITECNICO DIB
ARI,
I
TALIEL.
P
IERRELI
NGENIEUR,
T
RANE,
G
ROUPEI
NGERSOLLR
ANDH.
P
ANETTOP
ROFESSEUR A L’
UNIVERSITE DEL
ORRAINE(D
IRECTEUR DE LA THESE)
A.
A
UBRYM
AITRE DEC
ONFERENCES A L’U
NIVERSITE DEL
ORRAINE(C
O-D
IRECTEUR)
H.
B
RIL-E
LH
AOUZIM
AITRE DEC
ONFERENCES A L’U
NIVERSITE DEL
ORRAINE(C
O-
ENCADRANTE)
Centre de Recherche en Automatique de Nancy, UMR 7039 Université de Lorraine – CNRS
École Doctorale IAEM Lorraine
anything said is said BY an observer
Maturana, H.R., Varela, F.J., 1980. Cognitive Function in General, in: Autopoiesis and Cognition, Boston Studies in the Philosophy of Science. Springer Netherlands.
anything said is said TO an observer
Von Foerster, H., 2003. Understanding Understanding: Essays on Cybernetics and Cognition. Springer.
the only thing that meaning and intuition have in common is their obscurity
Chomsky, N., 1975. The Logical Structure of Linguistic Theory. Springer US.
l’ingegno, che è stato dato all’uomo per conoscere, ossia per fare
Vico, G., 2005. De antiquissima Italorum sapientia: con traduzione italiana a fronte. Ed. di Storia e Letteratura.
interpréter l’objet non pas en lui-même, mais par son comportement
Le Moigne, J.-L., 1994. La théorie du système général: théorie de la modélisation. Presses Universitaires de France-PUF.
la structure (c’est-à-dire l’ordre des parties) et la fonction (l’ordre des processus) sont
peut-être la même chose.
Von Bertalanffy, L., 1956. General systems theory.
la connaissance consiste essentiellement, en effet, non pas seulement à acquérir et à
accumuler des informations, mais encore et surtout [...] à les organiser et à les régler
par des systèmes d'autocontrôles orientés vers des adaptations, autrement dit vers
la solution de problèmes.
Acknowledgements
I would like to thank all the people who were more or less casually involved in the path to the construction of this work. All the discussions, debates and disputes I had during these years made this thesis and myself richer.
I would like to spend some more words to thank
• Hervé Panetto, Alexis Aubry and Hind El Haouzi for the opportunity they gave me and for the precious support during these years at CRAN and Trane and, generally, during my experience in France;
• Ludovic Pierrel to have accepted to replace my former enterprise tutor and to have guided me at Trane during this adventure;
• Professor Michele Dassisti for the inspiring discussions had during these years;
• Professors Aldanondo and Trajanovic, who accepted to be the official reviewers of the thesis; • Camille Salinesi to have accepted to be part of the jury;
• all the colleagues and the members of CRAN for the interesting discussions,
o special thanks to Gerard Morel for the interesting remarks about system theory, o special “sorry” to all the PhD and master students that I bored with my long remarks
and argumentations;
• all the colleagues that I had the luck to meet at Trane during my stay in France,
o special thanks to Sebastien Estublier for the essential help provided for the case study,
o as above, special “sorry” to all.
I would also give my special attention to Professor Didier Wolf, who welcomed me during my stay in France, at CRAN facilities.
6
Contents
Contents
CONTENTS ... 6
CHAPTER 1
INTRODUCTION ... 9
1
-‐
P
REFACE... 9
2
-‐
G
ENERAL INTRODUCTION... 9
3
-‐
I
NTRODUCTION TO THE PROBLEM STATEMENT... 12
4
-‐
A
NALYSIS OF THE INDUSTRIAL ISSUES:
THET
RANE SCENARIO... 12
5
-‐
C
ONTEXT AND RESEARCH QUESTIONS:
PV
ALTERNATIVES GENERATION AND EVALUATION... 21
6
-‐
C
ONCLUSIONS... 24
CHAPTER 2
A DESIGN KNOWLEDGE REPRESENTATION FRAMEWORK FOR PRODUCT
VARIETY (PV) ALTERNATIVES GENERATION ... 27
1
-‐
L
ITERATURE ABOUTPV
DESIGN APPROACHES:
LINKING THE VARIETY OF TWO DOMAINS... 28
1.1 -‐
Linking Real Customers with Customer Profiles ... 30
1.2 -‐
Linking Customer Profiles with Product Variants ... 33
1.3 -‐
Linking Product Variants with Process Variants ... 35
1.4 -‐
The gap in the literature: the lack of an unambiguous knowledge representation ... 36
2
-‐
D
ESIGN KNOWLEDGE REPRESENTATION... 39
2.1 -‐
Schools of Knowledge Representation ... 39
2.2 -‐
Anti-‐logicism, logicism and the ambiguity of the representation ... 40
3
-‐
O
UR APPROACH:
DESIGNKR
FRAMEWORK FORPV
ALTERNATIVES GENERATION... 43
3.1 -‐
Design KR framework ... 43
3.1.1 -‐
Conceptual model ... 43
3.1.2 -‐
A short instantiation of the experience concept ... 45
3.1.3 -‐
How the experience instances can be retrieved and connected ... 48
3.1.4 -‐
An algorithm to prove the non-‐ambiguity of the representation ... 49
3.2 -‐
From design KR to PV design: the generation of the PV alternatives ... 50
3.2.1 -‐
The discretisation of the domains ... 51
3.2.2 -‐
Testing the customer-‐process couples feasibility ... 52
3.3 -‐
Expected effects on the question RQ1 and on the industrial issues ... 54
4
-‐
C
ONCLUSIONS... 55
CHAPTER 3
EVALUATING THE PV ALTERNATIVES ... 56
1
-‐
O
VERVIEW ONPV
EVALUATION CRITERIA... 57
1.1 -‐
Index based on the customer requirements ... 58
1.2 -‐
Indexes based on the product features ... 58
1.5 -‐
The gap in the literature: the relation variety/cost ... 64
2
-‐
T
HE IMPACT OF THE VARIETY ON THE MANUFACTURING COSTS:
LOT STREAMING... 66
3
-‐
O
UR APPROACH:
PV
ALTERNATIVES EVALUATION... 68
3.1 -‐
About the relation between the variety and the costs ... 68
3.2 -‐
An approximation of the waiting time ... 72
3.3 -‐
The implementation of the new criterion for the PV evaluation ... 74
4
-‐
C
ONCLUSIONS... 76
CHAPTER 4
CASE STUDY: WATER COIL ASSEMBLY ... 77
1
-‐
T
HE MULTI-‐
DOMAINKR
FRAMEWORK:
A CASE STUDY... 77
1.1 -‐
The water coil knowledge represented in CATIA V5 ... 78
1.2 -‐
The design of the water coil variety ... 82
1.3 -‐
The unambiguity of the water coil knowledge ... 88
1.3.1 -‐
The two experiences represent the same measurements ... 88
1.3.2 -‐
The two experiences shares the representation of some measurements ... 89
2
-‐
W
ATER COIL VARIETY ALTERNATIVES:
GENERATION AND EVALUATION... 90
2.1 -‐
The step one: the structure of the data file and the constraints in Lingo14 ... 91
2.2 -‐
The step two: the interface with Lingo ... 93
2.3 -‐
The step three: the generation of the feasibility report file ... 95
2.4 -‐
The step four: the optimisation model generation ... 96
2.5 -‐
The two last steps: the solution of the optimisation model ... 97
2.6 -‐
Modification of the models to reduce the execution time of the solver ... 98
3
-‐
C
ONCLUSIONS... 99
CONCLUSIONS: LIMITS AND PERSPECTIVES OF THE PROPOSALS ... 101
1
-‐
G
ENERAL CONCLUSIONS... 101
2
-‐
R
ESEARCH CONCLUSIONS... 102
2.1 -‐
First research question (RQ1) ... 102
2.1.1 -‐
Limits of the proposals ... 103
2.2 -‐
Second research question (RQ2) ... 103
2.2.1 -‐
Limits of the proposals ... 104
2.3 -‐
Perspectives and possible improvements ... 104
3
-‐
I
NDUSTRIAL CONCLUSIONS... 105
3.1 -‐
First industrial issue (II1) ... 105
3.2 -‐
Second industrial issue (II2) ... 105
3.3 -‐
Third industrial issue (II3) ... 106
8
Contents
LIST OF ACRONYMS ... 108
LIST OF FIGURES ... 109
LIST OF TABLES ... 111
PERSONAL REFERENCES ... 112
REFERENCES ... 113
ANNEX 1: LINGO SYNTAX ... 120
ANNEX 2: ASSEMBLY SYSTEM FOR THE ANALYSIS OF THE VARIETY/COST RELATION .. 122
ANNEX 3: WATER COIL VARIETY GENERATION MODEL ... 131
Chapter 1 Introduction
1 -
Preface
This PhD thesis is the result of the collaboration between the Trane company and the Research Centre for Automatic Control (CRAN), Joint Research Unit of the University of Lorraine and the CNRS. This thesis is included in the CIFRE (Convention Industrielle de Formation par la REcherche) framework, i.e. the work is co-founded by Trane.
During the three years of works on this thesis, the thesis-related Trane context has been characterized by a project about the development of a new customizable product. This product was designed by an engineering team in the south of Europe and had to be manufactured in more than one Trane manufacturing plant, not only in Europe. The project represented two main challenges for Trane: the product knowledge transfer and the customer and manufacturing heterogeneity harmonization. Actually, these two project challenges became the motivation of the enterprise-university collaboration and so the origin of this thesis.
2 -
General introduction
Nowadays, in more and more market segments, high demanded volumes (mass-) and a large variety of requirements (-customisation) make the engineer-to-order approach and make-to-stock approach ineffective.
Indeed, the engineer-to-order approach is usually adopted when the customers have highly specific requirements. Therefore, at each order entry, new requirements are formalized and a new engineering stage should be performed. This strategy is plausible when low volumes of the products (i.e. of different products) are required, i.e. inversely, too many engineering stages should be performed.
Instead, the make-to-stock approach is usually adopted when the customer requirements are homogeneous. Therefore, at each order entry, the customers specify only the volume of the product they need. On the engineering side, all the work is already performed. Indeed, the products are expected to be already in stock before the order entry takes place. This strategy naturally fit when high volumes and low variety of the products are demanded.
Therefore, none of the above approaches can fit the mass-customisation scenario: i.e. high volumes and high customer requirement variety. Indeed, when the target of an enterprise is a customer segment with these characteristics, a make-to-order strategy is naturally adopted: the enterprise propose to the customer a set of already engineered products that, at the order entry, should be only manufactured. In order to adopt this strategy, enterprises need a different approach to the product design: the design for variety (ElMaraghy et al. 2013). By designing a set of products, namely a product variety (PV), in a single design stage, the enterprises can guarantee to the customers a good level of customisation and an appropriate responsiveness to high demanded volumes.
10
General introduction
the need of a method to design the variety (i.e. the set) and the products variants (i.e. the members of the set) at the same time.
This point is essential when the target of the enterprise is a customer set expressing a high degree of requirement variety. Indeed, in this case, it is not possible to design individually the variants before starting with the variety design stage, i.e. as for engineer-to-order, too many engineering stage should be required. Unfortunately, the individual design is the main requirement of all the reviewed methods for the PV design. And, in the reviewed methods, this is due to a lack of design knowledge representation, required to connect in an unambiguous way 1) the customer requirements to the product that should meet its requirements and 2) the products to the manufacturing process that is able to manufacture them. The 1) ambiguity of the customer profiles definition and 2) the lack of design knowledge hinder the current methods in literature to design a PV without an initial definition of the individual variants.
In order to cope with this lack, we propose, in this work, an unambiguous knowledge representation framework, a method to deploy it and a criterion to design and evaluate PV alternatives.
The dissertation will follow the structure presented in Fig. 1.1. In the first chapter (i.e. the following sections of the current one), the problem statement is discussed. In the second and third chapter, the research questions are treated. Both the chapters have the same structure: 1) literature to find existing answers for the addressed research question and identification of a gap in the literature; 2) literature to build our proposal; 3) our proposal. In the fourth chapter, a case study is presented. The detailed structure is the following.
• In this first chapter, the industrial issues (IIs in Fig. 1.1) are discussed. For each issue, the enterprise scenario is modelled and an analysis is performed to identify the context of the problems, i.e. the PV design. Starting from the analysis of the issues, in the second part of the chapter, the research context is detailed. The definitions of mass customization and so of the
design for variety allow to deal with the issues from a research viewpoint. From this
contextualization, the two research questions are identified: the first requiring a variety model including the knowledge from the customer, product and process domains; the second requiring a criterion to evaluate each PV alternative generated with the variety model.
• In the second chapter, the first research question is treated. An overview on works about the PV design is provided: the focus is on how the methods in literature allow to model the link between 1) the real customers and the customer profiles, 2) the customer profiles and the product variants and 3) the product variants and the process variants. An analysis of this literature allows to identify a gap about the lack of unambiguous design knowledge
representation (KR) in the method for the PV design. This lack does not allow to provide an
answer to the first research question. After an overview on works about the knowledge representation, by transposing the principles of the anti-logicist KR approach, our framework
framework on the identified PV design lack is showed. The result of the application is a set of
designed PV alternatives.
• In the third chapter, the first research question is treated. An overview on works about the PV design is provided: in this chapter, the focus is on how the methods in literature allow the evaluation of PV alternatives. The review of the research papers shows also in this case a gap: no-methods propose a criterion to take into account the manufacturing costs other than
the direct one. As shown by studying the nature of the variety/cost relation, this lack can
lead to wrong evaluations. A lot-streaming-based mathematical model allows to analyse this relation. On the basis of the result of this analysis, we propose a PV evaluation criterion that considers the effect of the process variety on the manufacturing costs.
• In the fourth chapter, the approaches to answer the two identified research questions RQ1 and RQ2 are applied on the industrial issues: a case study is presented. The formalisation of the knowledge relative to a water coil variety is shown. The instantiation of our framework is performed on a CAD software. Then a simulation of knowledge retrieval for a PV design stage is described. After a demonstration of the unambiguity of the KR, the application of the formalised design knowledge for the generation of PV alternatives is shown. The developed prototype is based on a Java tool that is interfaced with a mathematical solver to provide the PV alternatives and compare them to define the best PV.
At the end of the dissertation, a conclusion sums up the main points of the work. The impacts and the limits of the proposed solutions on the industrial issues and research questions are discussed. Moreover a discussion is presented on the perspectives about the research community and about the industrial application of the proposed approaches.
12
Introduction to the problem statement
3 -
Introduction to the problem statement
In the reminder of this first chapter of this dissertation, the motivation of the work is discussed. The structure of the chapter is the following (Fig. 1.2):
• the section 4 is dedicated to the analysis of the industrial issues (IIs): the enterprise is briefly introduced; an overview on the Trane products and services is given; then three industrial issues are discussed;
• the aim of the section 5 is to identify the research context in which these issues are treated and then to identify the research questions (RQs) from these industrial concerns.
Fig. 1.2 - role of the chapter in the thesis structure.
4 -
Analysis of the industrial issues: the Trane scenario
Trane is an industrial company that designs, manufactures and commercialises Heating, Ventilation and Air Conditioning (HVAC) systems and provides HVAC related services. Currently Trane is a business of Ingersoll Rand. In the commercial segment (i.e. hotels, universities, hospitals, restaurants and so on), Trane revenue is about $ 5-6 billions. The global presence of the company is organised in 4 geographic areas (Fig. 1.3): North America, Latin America, EMEIA (Europe, Middle East, India and Africa), and Asia Pacific. In these areas, Trane has more than 20 manufacturing locations, 250 service locations and about 400 business locations in more than 100 countries.
Fig. 1.3 - Trane manufacturing plants over the world
.
Trane products and services can be grouped in 6 main categories (Fig. 1.4):
• chillers: these machines are used to remove heat from the water; the removed heat can be released to the air (i.e. air-cooled chillers) or to the water (i.e. water-cooled chillers); some convertible machines can also heat the water; the range of power goes from 13 kW to 14 MW;
chillers can be equipped with scroll, screw or centrifugal compressors;
• airside: the machines in this category use the water coming from the chillers to treat the air that has to be distributed into the building; airside machines humidifies, dehumidifies, cools, heats and filters the air; larger machines (e.g. AHUs - Air-Handling Units) are for centralised control and terminal units (e.g. fan coils) are for distributed control of the airflow properties; Trane AHUs can handle airflows from 1000 to 250.000 m3/h;
• unitary: machines in this group merge the chillers and the AHUs functions in one single product; anyway, these machines provide lower power than chillers (i.e. the biggest provides up to 165 kW) and less refined air treatment option compared to the airside units;
• controls: this category includes all HVAC control systems for single units (e.g. fan coils, air-handling units) and the software for the centralised control of all building systems;
• services and parts and energy solutions: Trane provides services such as assistance for guaranteed performances, part supply, predictive maintenance, compressor restoring, remote system monitoring, etc.
14
Analysis of the industrial issues: the Trane scenario
Fig. 1.4 - Trane products and services
From the largest chiller to the smallest fan-coil, each one of the Trane products takes part to the air-handling system of a building. In this thesis, the water coil family representing one of the fan coil unit components (airside category) will be the core of most examples and especially the object of the test case in the application chapter. The main function of a water coil is to transfer the heat from the water to the air and/or vice versa. A further description of the coils is presented later in this dissertation. The choice of the water coil for the examples is due to three reasons:
1. the simple physical structure of the water coil makes easier and more understandable the presented examples; this feature does not impact the size of the treated case study; however, an extensive discussion on the size problem is presented at the end of the fourth chapter, when the impacts of the proposals are discussed;
2. the component is anyway complex; indeed, as in (p. 19 in (Von Bertalanffy 1956)), the complexity is due to the intensity and the non-linearity of the interactions between the system features;
3. the water coil represents a good compromise between the complexity of the component and its versatility; indeed, the water coil is used wherever a water-air heat transfer is needed, e.g. air-handling units.
The versatility of most of Trane products components is required by the commercial market that represents the Trane target. Indeed, Trane customers have highly specific requirements. Usually enterprises cope with this requirement variety by deploying an Engineer-To-Order (ETO) strategy, i.e. engineers design a brand new product at each order entry. Sectors that typically adopt this strategy are characterized by complex (and expensive) products and low volumes. Because of the required high volumes, the ETO cannot completely fit the Trane required responsiveness.
This high variety/high volumes scenario impacts the Trane design process. Indeed, the usual design stage at Trane results in a set of products with certain similarities that are addressed to a given set of customers. This Product Variety (PV) is a sort of menu or catalogue in which customers with different
a variant in the variety, the customer is ordering an already engineered product. In this way the PV allows Trane to avoid an engineering stage for each new customer (i.e. for the customer considered during the PV design).
The customer variety and the consequent PV design impact the order entry process. Indeed, during each order entry, the customer has to express his specific needs (for the scope of this dissertation, the eventual differences between the meanings of the terms “requirement” and “need” are not influent) and a product to meet this needs has to be selected (Fig. 1.5).
Fig. 1.5 - Trane product selection process on BPMN
The main stages of this selection process are the following.
• A customer describes his requirements and a seller interprets these requirements in order to link the customer with a customer profile described by a software selection tool. In each selection process, this interpretation provides the link between a real customer (set A in Fig. 1.6) and the customer profiles (set B in Fig. 1.6). This link is expected to be formal, i.e. each customer has a correspondent customer profile. Instead, in the Trane process, an ambiguity during this interpretation can happen: two sellers who interpret the needs of the same
customer can link his needs with two different customer profiles.
• Once the profile has been defined, the selection tool (in Fig. 1.7 a screenshot of the tool for the fan coils selection is shown) performs a research of the “right” product that can meet the customer profile requirements. The task performed by the selection tool provides the links between the customer profiles (set B in Fig. 1.6) and the Trane products (set C in Fig. 1.6). The term “right” is used because, once the customer profile is defined, the profile is expected to be linked with the best product (economic considerations included) the company can provide to meet the profile-related needs. At Trane, the selection tool can propose more
16
Analysis of the industrial issues: the Trane scenario
Fig. 1.6 - Trane product selection: building links from the real customers to the product variants.
For the sake of example, let us consider the selection of the appropriate fan coil to meet the customer’s needs. In Fig. 1.7, the selection tool for the fan coil variety is shown. The most complex part to be selected is the water coil. In order to make the tool performing a research among the fan coil variants, the seller has to characterise the customer profile as room temperature, humidity, water temperatures and so on. The tool produces several resulting coils. Then the customer should choose one of them according price, size, weight, noise level, power and other performances.
By focusing on the Trane product selection process, the first industrial issue (II1) can be described as follows:
II1 - If a customer describes its requirements to more than one seller then more than
one different resulting product can be proposed to the customer (for the same needs). Are the proposed product variants equally good for the customer? Is there a best alternative for the customer? Is there a best alternative for Trane? And so, given a set of customers, how to design a PV that represents the best way to cover the customers’ needs, i.e. the best subset C in Fig. 1.6?
Solving this industrial issue, for the simple instantiation of figure 1.6, means choosing between C1 and C2.
As shown in Fig. 1.3, Trane is present in four continents with its manufacturing plants. Often, the same customer profiles can be defined as targets for more than one manufacturing plant. This represents a second source of variety, this time on the manufacturing side. Indeed, the same customer profile can be linked with a product manufactured in two manufacturing side with their own manufacturing processes (e.g. drills or punching machines to manufacture a hole in a sheet metal) and constraints (e.g. cost and availability of raw materials).
During past years two strategies were adopted to deal with this manufacturing heterogeneity:
1. a global design strategy (Fig. 1.8): imposing a common design for each plant except for local legal and manufacturing feasibility constraints, e.g. regulation and norms on electric equipment, punching tool availability, local machine capacities and so on;
and manufacturing process features (e.g. punching tools); product and process engineers perform a sort of improvement loop until both agree on the PV design.
18
Analysis of the industrial issues: the Trane scenario
The aim of each one of these strategies is the harmonization of the manufacturing process heterogeneity with the customer profiles homogeneity. Starting from the experiences on the past PV design projects the following limitations can be highlighted.
Concerning the first strategy, on one hand it minimizes the product engineering effort but on the other hand it reduces the degrees of freedom of the process engineers by imposing a common
product design. Indeed, process engineers should propose product changes that 1) optimise the
usage of the local plant features (e.g. equipment, resources) and 2) preserve the satisfaction of the customer requirements. Unfortunately, this first strategy cannot take into account these optimisation opportunities because the product features, even if not directly impacting the customer requirements, have to be the same for each manufacturing plant.
Fig. 1.8 –Trane design and development process according global strategy 1.
The aim of the second strategy is to exploit all these optimization opportunities and so to let the process engineers design an optimal use of the plant resources. In this case, the same product can have different features that depend on the plant in which the product has to be manufactured. The manufacturing processes in each plant can be optimal because the constraints on the production are only related to the required product performances to meet the customer requirements, i.e. no constraints about the way to get these performances. On the other hand, in this case the reduction of
the product design efforts is not considered, i.e. product designers have to work separately for
each manufacturing plant. This means that different design stages to cope with the same customer requirements are performed.
Fig. 1.9 –Trane design and development process according strategy 2.
To sum up, both strategies tries to find a compromise between the minimization of the PV design efforts and the maximization of the process engineer degrees of freedom. The issues related with both the strategies can be summarized with the following industrial issue:
II2 - Is it possible to conjugate design effort and local manufacturing cost reduction?
In other words, how to link the product variety C and process variety D (Fig. 1.10) in order to impose to D, only the constraints that guarantee the satisfaction of the customer requirements? And consequently, how to find the best process variety, i.e., the best subset of D coming from different manufacturing plants?
Fig. 1.10 - Trane design process: building links from the product variants to the process variants
Solving this industrial issue, for the simple instantiation of figure 1.10, means choosing between C1
and C2.
With its PV design stage, Trane addresses a really wide market segments. The definition of these segments is done on the basis of the forecasted customer’s demand for each profile. The same definition determines the only target for the PV design. Therefore, even if many efforts are done to
20
Analysis of the industrial issues: the Trane scenario
fulfil a large set of customers, there are some customers with requirements that were not considered in the PV design stage, i.e. requirements related to profiles with an expected low demand.
In most sectors, e.g. automotive, the customer can only select one of the proposed product variants in the PV. No-further customisations are allowed after the end of the PV design stage. About this point, Trane represents a particular case, also in its own sector. If, during the selection process (Fig. 1.5), the tool performs a research without finding any variants meeting the customer’s needs, Trane accepts anyway the order. This acceptation is temporary. Indeed, the feasibility verifications, the design and the manufacturing cost estimations have to be performed.
This situation represents a special order (Fig. 1.11), i.e. the customer does not find a product fulfilling his needs in the already designed PV. In some cases, especially for smaller required modifications (e.g. particular room humidity and coil water conditions), the seller has enough experience to formalise these new needs and send them to the engineer team. For non-common request (e.g. a different shape for the fan coil case), the customer can discuss its requirements directly with the Trane engineers.
Fig. 1.11 – Trane order entry for special orders
By accepting the order, a new design stage is performed. The aim of this process is to generate a new product variant that fulfils the special requirements of the customer. During this phase, engineers stress on the reuse of the work performed during the PV design stage. All this new design stage strives for the maximization of the commonalities between the new required product variant and the ones in the designed PV. This design knowledge reuse is relative to both the product and the manufacturing process features. But, at Trane, even if the same knowledge used during the PV
design is also needed for the design of the special variant, a new design stage is performed.
II3 - At Trane, the special design stages can represent 20% of the orders of certain
product families. What is the right way to link the main design stage (i.e. related to the PV) with the secondary ones (i.e. for special orders)? Can a PV model adapt (Fig. 1.12) the product offer to the new customer requirements? If yes, how to model it?
Fig. 1.12 – Trane special order issue: stress on the knowledge reuse
To sum up, from the order entry process until the design stage, in this section, an overview and an analysis of how Trane cope with the variety has been presented. Three points have emerged. These issues represent improvable points of the Trane above discussed processes. In the next section, a contextualization of these issues in a research field is performed. This should allow to recognize the research field in which solutions that fit the Trane requirements can be retrieved.
5 -
Context and research questions: PV alternatives
generation and evaluation
What if technology made it possible for every one of the five thousand shirts to be customized while on the assembly line […] produced just as quickly as the five thousand identical shirts, yet at not greater expense? Starting from these words Davis in (S. M. Davis 1987) introduced for the first time the
concept of Mass Customisation (MC) for a shirt manufacturer. The two-sided nature of the MC concept can be better identified in (Tseng and Jiao 2001) or (Blecker et al. 2004): ideally MC is a business approach that want to fulfil individual customer’s needs having an organizational efficiency of a mass production company. Trane, as discussed in the first industrial issue, has high volumes (mass-) and a variety of customer needs to be met (-customisation(mass-). Therefore the Trane business can be considered in the MC context.
In order to follow the MC ambitions, an enterprise should be able both to provide a high level of product customization and to react with a reasonable time-to-market to cope with the high required
22
Context and research questions: PV alternatives generation and evaluation
volumes. Neither an engineer-to-order (ETO) approach nor a make-to-stock (MTS) approach can deal with this double requirement. The former approach can guarantee good levels of customisation but also leads to a large increase of the to-market. The latter approach can guarantee excellent time-to-market but also leads to inappropriate levels of customization. Therefore, the right approach is at the middle, i.e. make-to-order (MTO): enterprises design a variety of products and at the order entry only the manufacturing time impacts the time-to-market. In other words, the big deal is 1) to compress the duration of the engineering stage at each new customer order and 2) to propose to the customers a good level of customisation. As at Trane (see the section 1.1), one of the most common solutions is to design a Product Variety (PV) in place of lots of single products.
In the literature the “PV” concept can be associated to different terms, e.g. product family (Hong et al. 2008), configurable product (Aldanondo and Vareilles 2008) or product line (Pohl, Bockle, and Van Der Linden 2005; Mazo et al. 2012). The small differences between these terms are out of the scope of this work. Therefore, in the remainder of this thesis, we will use the following definition given by (ElMaraghy et al. 2013) because it is the most general one.
A variety and a variant are respectively defined as a number or collection of different things of a particular class of the same general kind and an instance of a class that exhibits usually slight differences from the common type or norm (ElMaraghy et al. 2013).
As discussed in the industrial issues, the PV design implies the modelling and the connection of knowledge (Fig. 1.13) coming from the customer, the product and the process domains (in this thesis, the term domain is used to define a set of pieces of knowledge): customer-product in the first issue; product-process in the second issue; new customer-customer in the third issue.
Fig. 1.13 - Links between domains involved in the PV design stage.
1. The first issue concerns the links between a variety of customers and the PV: if the customer-PV connections are not formalised then the product variant selection can be fuzzy (i.e. same customer and two sellers results in two variants) or far from the optimal one.
2. The second issue considers the connections of the PV with the process variety: if the model of the relations between the PV and the process variety is not formalised then the selection of
process engineer degrees of freedom.
3. The third issue considers the integration of a new customer variant into an existing customer variety: if a special customer is not integrated in the model of the customer variety then a new design stage is needed.
The variety modelling issues related to the industrial issues are shown in Fig. 1.14. At the top of the figure, the first and the second issues are modelled as connections between the real customer set (i.e. the target of the PV) and the manufacturing process set. Both the first issue and the second issue are about the lack of a formal model of the connection between the variety of the customers, the products and the processes. The first issue shows some lacks about the formalisation of the links between the customer domain (set A and B) and the product domain (set C). The effect is a quiet fuzzy product selection. On the other hand, the second issue is about the connections between the PV (set C) and the process variety (set D). The effect is the choice of some unbalanced product/process design strategies. The third industrial issue can be solved by the same solution to be developed for the first two issues: if a mapping is possible between varieties expressed in different domains then a mapping is possible between variety coming from the same domain (Fig. 1.14), i.e. the customer domain.
Fig. 1.14 - Representation of the industrial issues as mapping problem between variety representations: from different domains (1st and 2nd issues) or the same domain (3rd issue).
From this analysis of the relations between the industrial issues, the first research question can be formulated as follows:
24
Conclusions
RQ1 - How to model the variety in order to support a PV design process that at the
same time takes into account the knowledge that relates the customer profiles, the product variants and the manufacturing process variants?
By answering the first research question, a formalisation of the links between customers and products should be possible. These relationships should allow to have a complete control of the product selection (II1), i.e. for the same customer requirements only one variant should be proposed. Building the same mapping until the manufacturing processes should allow to consider product, process varieties and their impacts on the customer set requirements in the same model. Therefore it should be possible to constrain the manufacturing processes only on the product features that cannot be modified to meet the performances required by the customers. Doing so, each PV should emerge from the customer and the manufacturing constraint. This should allow both to minimise the product design effort and to maximise the local cost reduction opportunities (II2). Since a model to formalise the variety from different domains, the integration of a new customer in the older PV model (II3) should become possible. The aim is to understand if the formalised knowledge is enough to meet the new customer requirements or some new piece of knowledge has to be added to fulfil them (i.e. the new customer has no corresponding product variants).
Once it is possible to connect variety model coming from different domains, starting from a given customer set a designer should be able to propose process alternatives (e.g. D1 and D2) that can meet
the requirements of the customers. Once it is possible to generate these process variety alternatives, the deployment of some criteria to compare them is needed. Now, let us introduce the second research question:
RQ2 - How to compare different variety alternatives, i.e. process varieties that allow
to manufacture PVs able to meet the same customer variety?
Here the objective is to find one or more criteria to compare the alternatives generated by answering to the first research question. These criteria should guarantee a sound approach to establish which is the best product variant for a given customer (II1 and II3) and which is the best process variant for a given product variant (II2 and II3). Notice that the criteria are not expected to optimise individually the variants. Indeed, the solution at the question RQ2 should provide a metric to evaluate the variety as a whole.
6 -
Conclusions
In this first chapter the discussion about the industrial issues has been presented (Fig. 1.15). After a description of the scenarios and a contextualisation of the industrial issues, in the last section the two research questions that will be treated in this dissertation have been formulated.
Fig. 1.15 - results of the first chapter.
Both the questions (Fig. 1.16) concern aspects of the PV design modelling: 1) the first question copes with the generation of a model to support a PV design that takes into account at the same time the customers, the products and the manufacturing processes. 2) The second question deals with the development of a criterion (or more criteria) to evaluate the PV alternatives generated during the PV design.
Fig. 1.16 - Illustration of the research questions
In the following two chapters the research questions are treated sequentially. According the different viewpoints, in each chapter the research works about the PV design are analysed differently.
• In the chapter 2, the focus is on how the methods in the literature cope with 1) the customer profile formalization and 2) the representation of the links between the real customers, the customer profiles, the product variants and the process variants. By identifying a gap in the reviewed works, a framework for the design knowledge representation is proposed. Finally the implementation of this framework on the PV alternative generations is discussed.
• In the chapter 3, the focus is on how the methods in the literature cope with the evaluation of the PV alternatives. The analysis of the nature of the variety/costs relations will allow the
26
Conclusions
identification of a gap in the works in literature, From the result of this analysis, the development of a more comprehensive criterion to evaluate the PV alternatives is presented. Finally, in the chapter 4, the framework and the criterion are tested on the design of the variety of a HVAC system component to assess the impacts on the industrial issues.
Chapter 2 A design knowledge representation
framework
for
Product
Variety
(PV)
alternatives generation
The aim of this chapter is to review the works about the PV (Product Variety) design and to propose an answer to the first research question:
RQ1 - How to model the variety in order to support a PV design process that at the
same time takes into account the design knowledge that relates the customer profiles, the product variants and the manufacturing process variants?
In the first section of this chapter, a literature review about the PV design is presented: the focus here is on how the presented methods link the variety representations. In other words, the issues treated in the papers below are classified on the basis of the links between the varieties (real customers, customer profiles, product variants and process variants) that are involved in the PV design stage. At the end of this section a discussion about the applicability of the methods in the literature is presented.
After the identification of a gap in the literature, the aim of the second section is to find works in literature that can help to bridge this gap. An overview on works about the Knowledge Representation (KR) is detailed. The purpose is to select and use certain KR principles as the foundations of the solution to answer the question RQ1.
In the third section of the chapter, our proposal to answer the question RQ1 (Fig. 2.1) is detailed. A simple instantiation is shown and the impact of the deployment of the proposals on the question RQ1 and on the industrial issues is discussed.
28
Literature about PV design approaches: linking the variety of two domains
Fig. 2.1 - role of the chapter in the thesis structure.
1 -
Literature about PV design approaches: linking the
variety of two domains
In this section an overview of the method for the PV design is presented. The literature about PV design represents more than 20 years of works on all the aspects of the variety design and development process. Generally a PV design approach can be classified according to three features (Simpson, Siddique, and Jiao 2006; Fujita and Yoshida 2004): the type of variety
representation, the decomposition of the design stage and the input of the design stage.
During the PV design stage, the 1) variety representation (Simpson, Siddique, and Jiao 2006) can be based either on a module selection (i.e. module-based design) or on the value definitions of a set of product related parameters (i.e. scale-based design). For instance, let us consider the AHU example. If the variety is characterized by the presence/absence of one or more components (e.g. humidification module, heat recovery module) then the design is module-based. If the variety is characterized by the values of some particular attributes of the AHU system (e.g. weight, power, materials) then the design is scale-based.
An approach to the PV design process can classified according the 2) decomposition of the design stage (Fujita and Yoshida 2004). Indeed, the PV design stage can be performed in one step or two
steps. In the first case, the two steps are performed simultaneously. In both cases, the output of the
PV design stage is the definition of the optimal non-shared modules or parameter values for the PV. At the end of the PV design stage, the optimal set of product variants (i.e. the PV) is obtained. When a two-steps approach is performed an intermediate stage is required. This stage is called Product
Platform (PP) design. The output of this stage of the PV design process is the optimal set of modules
or attributes values that should be shared between the variants in the PV, i.e. the optimal PP. A PP is a set of modules or parameter values that is shared between the variants in the PV. If all the variants in a PV share the same modules or attributes values then the PV is defined as a single-platform PV:
e.g. all the laptops share the same keyboard and trackpad; all the air conditioning units share the same sheet metal case; all the water coils share the same tube thickness. A PV can be based on more than one platforms (multi-platform PV): all the laptops share the same keyboard X, the 30% of these laptops share the trackpad A, the 70% share the trackpad B; the laptop family is based on two platforms, the first one is represented by the keyboard X and the trackpad A and the second one by the keyboard X and the trackpad B. If we consider the water coil example: all the coils share the same aluminium for their fins; the 50% of the coils share the fin profile A and the remainder of the variants share a fin profile B; the difference about the fin profile determines the two platforms which the PV is based on. A PP can be used for more than one PV.
Finally, a PV design approach can be classified according to the type of 3) input of the design stage (Simpson, Siddique, and Jiao 2006):
• Bottom-up PV design: this approach of PV design requires that a set of individual products has been already designed; the aim is then to maximize the commonalities and to minimize the negative effects on customer requirements, i.e. the commonality maximization alters the product performances and so it can alter the effects on customer requirements;
• Top-down PV design: this approach of PV design does not require an already designed set of products; the design stage starts with a given set of customer requirements related to customer profiles; then the product variant are specifically developed for the customer set, i.e. not designed separately and then modified as for the bottom-up approach.
The approaches reviewed in the following subsections are analysed with the focus on which domains links is considered (Fig. 2.2).
1. Real customers to customer profiles (section 1.1): the customer requirements have to be translated into product expected behaviours, i.e. performances. The formalization of this link includes all topics about the customer involvement into the PV design. Usually this class of issues deals with the analysis of the voice of the customer (VOC) and the customer clustering. These analyses are usually followed by the formulation of the relations between the expected performances and the customer demand, i.e. how the customer’s purchase decision is impacted by the performances provided by a variant in the PV.
2. Customer profiles to the product variants (section 1.2): it is about the transformation of performance requirements into product design variables, i.e. parameters or modules about the physical representation of the product variants. Concerns in this stage are called PV design issues. Most of the works about this class of issues includes the management of variant commonalities in the PV design.
3. Product variants to the variants of manufacturing processes (section 1.3): The third stage is about the impacts of the PV on the manufacturing processes and the supply chain. Topics about the link between the product and the process domain are defined as back-end issues. Most of works on these issues are about manufacturing and assembly processes design and supply chain design.
30
Literature about PV design approaches: linking the variety of two domains
Fig. 2.2 - Domain connections to be reviewed and section numbers of the reviews.
In the last part of this section (section 1.4), a discussion about the applicability of these approaches to answer the question RQ1 question is reported.
1.1 - Linking Real Customers with Customer Profiles
Concerning the first link, most of works in the literature use different techniques such as data mining (Fayyad, Piatetsky-Shapiro, and Smyth 1996), fuzzy logic (Slowinski 1998), conjoint analysis (Green and Srinivasan 1978), and quality function deployment (QFD - (Akao 2004)) to analyse the real customer requirements and interpret them. More than the others, some of these techniques (e.g. QFD) are naturally used for the customer requirement transformation. The others have been transposed for the use in the PV design stage (e.g. data mining). The aim of these methods is to assess how the product performances and/or features impact the customer’s purchase decision (i.e. the forecasted customer demand) and so the expected profit.
These techniques can be applied during each PV design approach: modular and scale based (e.g. modules can be used in place of product features); top-down/bottom-up and one-/two-steps because the decisions about the product platform or variety are not made at this stage (i.e. here the aim is to define the targets of the design stage).
Method based on conjoint analysis
Conjoint analysis allows to represent the customer requirements as relative importances given to a product feature or performances. Roughly, this characterisation allows to approximate the customer satisfaction as a customer utility function (U),
where I is the importance of the feature or performance i; x is the value of the feature or performance i; N is the number of features and/or performances.
For instance, in (Ferguson, Olewnik, and Cormier 2011), the use of the conjoint analysis for the design and development of a MP3 player is investigated. Here the aim is to provide a method to
connect the marketing data coming from the conjoint analysis to the engineering domain. A customer segmentation and an attribute prioritisation for each segment allow the authors to determine where (i.e. which product feature) a customisation is required.
The two main comments that can be expressed about the conjoint analysis are the followings.
• If the customer expresses its preferences as product features, he is performing a product engineer task (at the right of Fig. 2.3), i.e. the variety that is represented is in the domain of the product and so it is not modelling the customer profiles.
• if the performances (seen as expected effects of the product on the customer environment) are considered, then the first point is not still valid. But, anyway, 1) if the representation of the preferences aims to identify which is the performance to be maximized in all the variants, then the variety is still not represented: the maximisation is valid for each customer and so it is not representing the variety. Moreover, 2) let us consider
o the utility as proportional to the price that the customer is willing to pay
o and that the product that maximizes the utility costs more than the price that the customer is willing to pay for that level of performances.
Also in this case, the maximization limits the representation of the variety, i.e. all the product performances that can correspond to a utility are not represented.
Fig. 2.3 - the different representations of the variety performed by the customer.
Method based on data mining
Data mining is a technique that allows to identify some patterns between variables, starting from a certain amount of data. Customers’ data can also be collected from the internet like in (Tucker and Kim 2008): the authors develop a system for connecting the market demand analysis with the PP and the PV design. Data mining can be used to analyse the raw data from the Internet. The aim of the analysis (i.e. cleaning, transformation, pattern discovery and evaluation) is to build mathematical relations about the effects of the product features on the customer demand. This technique allows the calculation of the willingness to pay of the customers for given features. Moreover expected profits can be evaluated on the basis of the selected product feature set. The latter will represent the target in the engineering level. At the engineering level the architecture is related with the design constraints and the costs in order to find the best PV to be developed.
32
Literature about PV design approaches: linking the variety of two domains
The same first observation done for the conjoint analysis can be expressed for the data mining: if the customers talk about the product, the variety represented is still about the product domain and about the customer profiles.
Method based on QFD
The QFD is a matrix to represent connections of the voice-of-customer with the engineering view of the product-related requirements.
The use of the QFD for connecting marketing information to the engineering domain has been investigated in (Kazemzadeh et al. 2009) and in (Jariri and Zegordi 2008). In (Kazemzadeh et al. 2009), authors propose a five-steps procedure to integrate marketing and QFD for PV design. 1) A first conjoint analysis is performed for prioritising the customer requirements and to bridge the gap with the designers. 2) A two-steps clustering procedure is applied to identify homogeneous set of customers. 3) A conjoint analysis is then performed for each cluster. 4) The traditional QFD is applied to each segment and to all customers. 5) They propose three criteria to assess which one between a general product or a product for each segment represents the best choice. Authors in (Jariri and Zegordi 2008) merge the QFD use with a mathematical modelling to integrate the customer requirements in the PV design. The first QFD table, i.e. customer requirements to technical requirements, offers a vision of the relations between the customer satisfaction and the product functions. The second QFD table, i.e. technical requirements to component characteristics, provides different alternatives to achieve the required functions. Also in this case, the mathematical problem aims to maximise the customer utility (characterisation of the customer’s will of purchase) and to minimise the cost of the PV.
Also in this case, the same observation for the techniques reviewed so far is valid. Moreover, the clustering of the customers allows to provide a better vision of the variety compared to the simple conjoint analysis. The issue is about the number of QFD stages that is equal to the number of the variants to design.
Method based on fuzzy logics
Many other works deploy customer analysis using fuzzy logic to take into account reasoning that is not fixed and exact, i.e. approximate. Indeed, fuzzy logics, if compared to Boolean (i.e. preference expressed as “true” or “false”) techniques, are more expressive because allow to represent a partial truth, e.g. “80% true”. Examples of how fuzzy logic can be used for customer analysis in PV design are the following (Barajas and Agard 2009):
• customer clustering (using fuzzy clustering), to evaluate similarities among customer requirements;
• satisfaction level (using fuzzy goal programming), to assess the fulfilment level of the engineering design requirements; fuzzy logic is used to provide a better representation of the natural language;
• prioritisation of customer demands (using fuzzy inference), to fit the fuzziness of the voice of the customer;
• fuzzy QFD (using fuzzy numbers), to improve the definition of the links between customer requirements and the engineering characterisation of the product.
